1. Field of the Invention
The present invention relates to an ink jet recording head and ink jet recording apparatus for use in an ink jet printer, particularly in a bubble jet printer for utilizing a bubbling phenomenon to discharge an ink, and the like.
2. Description of the Related Art
A bubble jet recording system comprises: using a heating element to locally heat a liquid in a channel and generating a bubble; utilizing a high pressure generated during bubbling; pushing and discharging a liquid droplet from a microfine discharge port; and attaching the liquid droplet to a recording paper or another recording material to record an image. An ink jet recording head for use in recording the image by the bubble jet recording system generally includes a microfine discharge port, channel, and heating element disposed in the channel.
In order to use such ink jet recording head and record the image with a higher colorfulness, a technique of discharging the microfine liquid droplet with a high density is required. Therefore, it is basically important to form a microfine channel and heating source. Therefore, for the ink jet recording head of the bubble jet recording system, a method of utilizing simplicity of a head structure and fully using a photolithography technique to prepare a high-density head has been proposed (e.g., Japanese Patent Application Laid-Open No. 8-15629, and the like). Moreover, in order to adjust a discharge amount of liquid droplets so that microfine liquid droplets can be discharged, a heating element having a larger calorific value in a middle portion than in an end has been proposed (see Japanese Patent Application Laid-Open No. 62-201254).
As the heating element for use in the ink jet recording head, a tantalum nitride thin-film resistor with a thickness of about 0.05 xcexcm is usually used, and liquid is bubbled by Joule heat generated during energizing of the resistor. In this resistance heating element, in order to usually prevent the surface of the resistance heating element from being damaged by cavitation, an anti-cavitation layer formed of Ta or another metal having a thickness of about 0.2 xcexcm is disposed via SiN or another insulator having a thickness of about 0.8 xcexcm.
Moreover, in Japanese Patent Application Laid-Open No. 64-20151, a so-called multi-nozzle ink jet recording head is disclosed in which a plurality of longitudinal and transverse wires are disposed on a substrate, a rectifier element for passing a forward current and thereby generating the heat is disposed in a plurality of intersections of the wires, and discharge ports are disposed in a matrix form. Furthermore, in Japanese Patent Application Laid-Open No. 57-36679, an ink jet recording head is disclosed in which a plurality of diodes are disposed as heating elements in the matrix form on the substrate. In the diode, heat can be generated by passing electricity in a forward direction, and electricity cannot be passed in a reverse direction.
Additionally, in Japanese Patent Application Laid-Open No. 5-185594, another ink jet recording head is disclosed. The head is constituted by disposing a diode, and an electrothermal conversion element connected to the diode and disposed as the heating element in the matrix form on a head substrate so that the electrothermal conversion element can selectively be driven, or is constituted by disposing a logic circuit constituted of a shift register portion, latch portion, and logic circuit, and the electrothermal conversion element connected to the logic circuit on the same substrate so that the electrothermal conversion element can selectively be driven.
In most of conventional ink jet recording heads, a heating element, diode, logic circuit portion, and the like are simultaneously constituted and manufactured on a silicon substrate by a semiconductor process (e.g., an ion injecting method). In the manufacturing method using such semiconductor process, when the ink jet recording head having a relatively small number of discharge ports is manufactured, a compact constitution can advantageously be manufactured in a single step. However, a so-called full multi-head has a length, for example, of 12 inches (about 30 cm), which extends over a full width of a recording paper. When a necessary element is integrally formed in such a broad range by the semiconductor process, it is difficult to use a usual silicon wafer. Therefore, when the full multi-head is manufactured using the semiconductor process, a manufacturing cost possibly increases.
Then, when a non-linear element able to be manufactured without using a conventional semiconductor process can be used to constitute the circuit for selectively driving heating elements disposed in a matrix form, a longitudinal ink jet recording head like a full multi-head can possibly be provided at a low cost.
As the nonlinear element, a metal insulator metal (MIM) element for conventional use in a liquid crystal is known. This is a nonlinear element having MIM type electrical characteristics in which a resistance value during application of a low voltage indicates a high value regardless of polarity as compared with the resistance value during application of a high voltage. When the MIM element is used in the liquid crystal, a power for generating a power density of about 1 W/m2 is usually supplied. On the other hand, in the ink jet recording head of the bubble jet recording system, the power for generating a power density of about 0.1 GW/m2 or more needs to be supplied to the heating element. Therefore, for use of the MIM element in selectively driving the heating element, a large amount of power which has not heretofore been supplied needs to be supplied to or via the MIM element.
When a voltage applied to the MIM element is increased, it is possible to increase the power supplied to or via the MIM element to some degree. However, the voltage applied to the MIM element having a constitution similar to the conventional constitution is increased, and then there is a fear that the MIM element is adversely affected by a strong electric field. Moreover, there is a fear that the MIM element itself is adversely affected by a temperature rise by the heat generated by the MIM element. There is a fear that the electric field or an electrical current is concentrated particularly in an edge portion or a step portion of an electrode pair of the MIM element and a remarkably high heat is locally generated. There is further fear that the MIM element is adversely affected by the locally generated heat.
An object of the present invention is to reduce an adverse effect onto the nonlinear element by the heat or the electric field generated during supply of a power for producing a large power density with respect to the nonlinear element for selectively driving heating elements disposed in a matrix form in an ink jet recording head of a bubble jet recording system.
Another object of the present invention is to use a nonlinear element in a circuit for selectively driving heating elements disposing in a matrix form so that a longitudinal ink jet head can be provided at a low cost.
To achieve the aforementioned objects, according to the present invention, there is provided an ink jet recording head comprising: heating means for generating a heat energy to be utilized for discharging an ink; and a nonlinear element for driving the heating means, having MIM type current/voltage characteristics in which a resistance value during application of a low voltage indicates a high value regardless of polarity as compared with the resistance value during application of a high voltage, wherein the nonlinear element has an electric field relaxing structure for relaxing generation of a locally strong electric field in the nonlinear element.
The nonlinear element having the MIM type electrical characteristics is used, and thereby the heating means disposed in the matrix form can selectively be driven with a relatively simple constitution in which the nonlinear element is disposed in an intersection of a vertical electrode and a transverse electrode and connected to both electrodes. That is, when voltages opposite to each other in polarity are applied to one of a plurality of vertical electrodes and one of a plurality of transverse electrodes in the circuit constituted as described above, an electrical current is passed only to the heating means in the intersection of the vertical and transverse electrodes, and the heating means can selectively be driven.
When the voltage is applied to the nonlinear element as described above, the electric field formed in the element does not necessarily become uniform, and the locally strong electric field is formed. To solve the problem, the nonlinear element includes the electric field relaxing structure for relaxing the locally strong electric field, and can therefore bear the formed electric field with a relatively high power density.
Moreover, the nonlinear element constituted as described above can preferably be used in selectively driving the heating means of the ink jet recording head, which needs to be driven by supply of a relatively high power. Furthermore, when the nonlinear element is used, the selectively driven heating means disposed in the matrix form can relatively simply be constituted as described above. Additionally, the nonlinear element can be manufactured without using a semiconductor process. Therefore, a relatively longitudinal ink jet recording head can be manufactured at a low cost.
Some of these nonlinear elements such as MIM element and varistor have a constitution in which a pair of electrodes are disposed opposite to each other. For the use of the nonlinear element constituted as described above, it is known that the locally strong electric field is formed in an outer periphery of an opposite portion of the pair of electrodes. The pair of electrodes are structured such that an interval between the pair of electrodes increases in the outer periphery of the opposite portion of the pair of electrodes. Thereby, a strength of the electric field in the outer periphery is weakened, and the locally strong electric field can be relaxed. That is, this structure can be formed as the electric field relaxing structure. Additionally, in the present invention, the outer periphery of the opposite portion of the pair of electrodes is a part of the nonlinear element.
Moreover, according to the present invention, there is provided an ink jet recording head comprising: heating means for generating a heat energy to be utilized for discharging an ink; and a nonlinear element for driving the heating means, having MIM type current/voltage characteristics in which a resistance value during application of a low voltage indicates a high value regardless of polarity as compared with the resistance value during application of a high voltage, wherein the nonlinear element has a pair of electrodes disposed opposite to each other, and an interval between the pair of electrodes is larger in an outer periphery of an opposite portion of the pair of electrodes than in any other portion of the opposite portion.
As the nonlinear element for use in the ink jet recording head of the present invention, an MIM element is preferably which comprises a lower electrode disposed on a substrate, an insulating thin film disposed on the lower electrode, and an upper electrode disposed on the insulating thin film.
When the MIM element is used, an insulating layer is disposed between the insulating thin film and the upper electrode, the insulating layer has a first hole via which the insulating thin film is exposed in the vicinity of a middle of the opposite portion and which is tapered downwards in the opposite portion of the upper and lower electrodes, and the upper electrode has a downward protrusion having a downward convex shape for engaging in the first hole.
The upper electrode has a downward protrusion having a downward convex shape for engaging in the first hole tapered downwards in the opposite portion of the upper and lower electrodes constituting the MIM element. In the constitution, the interval between the electrodes increases in the outer periphery of the opposite portion of the electrodes, and this structure functions as the electric field relaxing structure.
The nonlinear element itself can be used as the heating means. Particularly, when the nonlinear element is the MIM element having the insulating layer as described above, a channel for introducing an ink to the vicinity of the MIM element, and a discharge port for discharging the ink can be disposed on the MIM element. In the constitution, when a depth of the first hole is adjusted, a distance between the discharge port and the MIM element can be adjusted to be adequate.
Moreover, a resistance heating element connected in series with the nonlinear element may be disposed as the heating means. In this case, particularly when the nonlinear element is the MIM element having the insulating layer as described above, a second hole for exposing a part of the substrate is formed in the insulating layer, and the upper electrode is extended downwards onto the substrate along the second hole. Moreover, the resistance heating element is connected to the upper electrode and disposed in this portion, and a channel for introducing an ink to the vicinity of the resistance heating element and a discharge port for discharging the ink can be disposed on the resistance heating element. In this constitution, when the depth of the second hole is adjusted, the distance between the discharge port and the MIM element can be adjusted to be adequate.
Moreover, the resistance heating element may be connected to the upper electrode and disposed on the insulating layer. In this case, the insulating layer functions as a heat accumulating layer of the resistance heating element. Therefore, temperature in the vicinity of the resistance heating element is effectively raised, and a discharged liquid can efficiently be bubbled. Furthermore, since the insulating layer is disposed between the resistance heating element and the substrate, temperature rise of the substrate by heat generation of the resistance heating element is inhibited, the heating of the MIM element disposed on the substrate is inhibited, and adverse effect by the heating can be reduced.
Additionally, the resistance heating element may be connected to the lower electrode, disposed on the substrate, and coated with the insulating layer. In this case, since the insulating layer functions as a protective layer of the resistance heating element, it is unnecessary to dispose a new protective layer.
The nonlinear element having the MIM type current/voltage characteristics for use in the ink jet recording head according to the present invention can preferably be used in selectively driving the heating means disposed in the matrix form as described above. Therefore, the present invention can preferably be applied to the ink jet recording head having a matrix electrode constituting a matrix circuit for applying the voltage to the heating means. Moreover, since the nonlinear element is disposed in the intersection of the matrix electrodes, the heating means disposed in the matrix form can preferably selectively be driven.
The present invention can preferably be applied to the ink jet recording head in which film boiling is caused in the ink by the heat energy and the ink is discharged.
Moreover, according to the present invention, there is provided an ink jet recording head comprising: heating means for generating a heat energy to be utilized for discharging an ink; and a nonlinear element for driving the heating means, having MIM type current/voltage characteristics in which a resistance value during application of a low voltage indicates a high value regardless of polarity as compared with the resistance value during application of a high voltage, wherein the nonlinear element comprises an insulating thin film, and a pair of electrodes disposed opposite to each other via the insulating thin film, and at least a portion of the pair of electrodes in contact with the ink is formed of a chemically stable conductor.
Thereby, even when the electrode constituting the MIM element contacts the ink, the electrode can be prevented from being damaged by an electrochemical action.
According to the present invention, there is provided an ink jet recording apparatus comprising: at least the aforementioned ink jet recording head in which an ink discharge port for discharging an ink is disposed opposite to a recording surface of a recording material; and conveying means of the recording material.